Method and apparatus for transmit signal power control and discovery signal resource multiplexing in wireless communication system

ABSTRACT

A method for transmitting and receiving a signal in a base station of a mobile communication system according to an embodiment of the present specification comprises the steps of: generating power control information for device to device (D2D) communication for a terminal; and transmitting, to the terminal, a message including an indicator indicative of a power control mode of the terminal in accordance with the generated power control information. In accordance with a method for controlling transmit power of a terminal and a method for selecting a transmit resource in a mobile communication system provided in an embodiment of the present specification, mutual interference between the device to device communication and cellular communication can be reduced, and the communication efficiency can be improved.

TECHNICAL FIELD

An embodiment of the present specification relates to a wireless mobilecommunication system, and in particular, to a UE operation including atransmission power control procedure and a multiplexing procedure of theUE in a system where a device-to-device communication technology and awireless cellular communication technology are used together, and to abase station operation corresponding thereto and an apparatus thereof.

BACKGROUND ART

A device to device (D2D) communication technique which allows directcommunication with another UE existing around the UE has emerged toprovide a more efficient service using a wireless mobile communicationsystem. A device to device communication technology may perform deviceto device communication through a discovery operation by a UE fordiscovering what kind of UEs are present around the UE and through adirect communication operation by the UE with a UE necessary forcommunication. As such, when the direct communication is performed bythe device to device communication, a relatively small amount ofwireless resource can be used in comparison with the communication usingthe conventional wireless network and a base station, and thus thewireless resource efficiency is improved. In addition, since a methodfor discovering UEs around the UE is supported, information required inaccordance with the position of the UE and characteristics thereof canbe provided to each UE, and thus new services such as an advertisementservice, a Social Networking Service (hereinafter, referred to as SNS),etc. can be created and service efficiency thereby can be improved.Currently, a Long Term Evolution Advanced (hereinafter, LTE-A) systemalso requires support for the device to device technology and technicaldiscussions therefor are under way.

The device to device communication may communicate using the samefrequency band as does a conventional cellular communication which usesa base station. When the device to device communication uses the samefrequency band as does the cellular communication, communication can beperformed by dividing the communication on a time and frequency axis inorder to solve a mutual interference problem. However, when a UEperforms the conventional cellular communication, control informationsuch as ACK/NACK, Scheduling Request (SR), Channel Quality Indicator(CQI), etc. can be periodically transmitted to the base station so thatthe frequency multiplexing may be required between the device to devicecommunication and the cellular communication as well as multiplexing ona time axis. At this time, when the UE performing the device to devicecommunication performs data transmission using an arbitrary transmissionpower, a problem may occur where in-band emission power thereby canprovide a relatively larger noise impact to other UEs than the D2D UEwhich should receive the transmission. Thus, in a case where the deviceto device communication technology and the wireless communicationtechnology are used together, in-band emission power due to the D2Dsignal transmission by the UE using the D2D technology in a system maycause a problem of noise in a cellular transmission, and thus the studyfor the situation is required.

DISCLOSURE OF THE INVENTION Technical Problem

In an embodiment of the present specification which is to solve theproblems described above, there is provided a method and an apparatusfor operating a UE and a base station required for performingcommunication between each of a plurality of UEs using a D2D technologyor communication between a UE using the D2D technology and a cellular UEwithout causing a degradation in the system performance due to in-bandemission power in a mobile communication system.

Solution to Problem

In order to achieve the purpose, according to an embodiment of thepresent specification, a method for transmitting and receiving a signalby a base station of a mobile communication system is provided. Themethod includes: generating power control information for device todevice (D2D) communication for a UE; and transmitting, to the UE, amessage including an indicator indicative of a power control mode of theUE in accordance with the generated power control information.

According to another embodiment of the present specification, a methodfor transmitting and receiving a signal by a base station of a mobilecommunication system is provided. The method includes: receiving amessage including an indicator indicative of a power control mode of theUE from a base station in device to device (D2D) communication for theUE; and transmitting a D2D signal based on the received message.

According to another embodiment of the present specification, a basestation for transmitting and receiving a signal in a mobilecommunication system is provided. The base station includes atransceiver that transmits and receives a signal to and from a UE; and acontroller that controls the transceiver, generates power controlinformation for device to device (D2D) communication for a UE, andtransmits a message including the indicator indicative of a powercontrol mode of the UE according to the generated power controlinformation to the UE.

According to another embodiment of the present specification, a UE fortransmitting and receiving a signal in a mobile communication system isprovided. The UE includes: a transceiver that transmits and receives thesignal to and from at least one of a base station and another UE; and acontroller that controls the transceiver, receives, from a base station,a message including an indicator indicative of a power control mode ofthe UE in a device to device (D2D) communication for the UE, andtransmits a D2D signal based on the received message.

Advantageous Effects of Invention

In accordance with an embodiment of the present specification, a methodfor controlling transmission power by a UE and a method for selecting atransmission resource in a mobile communication system is provided sothat the mutual interference between the device to device communicationand cellular communication can be reduced, and communication efficiencycan be improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing a state where device to device communicationis supported in a wireless communication system according to anembodiment of the present invention;

FIG. 2 is a diagram showing a state where D2D transmission and cellulartransmission are multiplexed using a Time Division Multiplexing (TDM)scheme according to an embodiment of the present invention;

FIG. 3 is a diagram showing emission power when transmitting a signal bya UE according to the embodiment of the present invention;

FIG. 4 is a diagram for explaining an operation of performing powercontrol by a UE according to a UE transmission power for the discoverysignal Control period;

FIG. 5 is a diagram for explaining a power control operation by a UE fora discovery resource region divided according to two transmission powercontrol methods different from each other;

FIG. 6 is a diagram for explaining a power control operation by a UE fora discovery resource region which is divided based on the position of aUE;

FIG. 7 is a diagram explaining an operation of controlling, by a basestation, a transmission power for the discovery signal of a UE fordownlink control channel information;

FIG. 8 is a flow chart illustrating an operation of a base stationaccording to a first embodiment of the present invention;

FIG. 9 is a flow chart illustrating an operation of a UE according to afirst embodiment of the present invention;

FIG. 10 is a flow chart illustrating an operation of a base stationaccording to a second embodiment of the present invention;

FIG. 11 is a flow chart illustrating an operation of a UE according to asecond embodiment of the present invention;

FIG. 12 is a flow chart illustrating an operation Of a base stationaccording to a third embodiment of the present invention;

FIG. 13 is a flow chart illustrating an operation of a UE according to athird embodiment of the present invention;

FIG. 14 is a flow chart illustrating an operation of a base stationaccording to a fourth embodiment of the present invention;

FIG. 15 is a flow chart illustrating an operation of a UE according to afourth embodiment of the present invention;

FIG. 16 is a diagram showing a configuration of a base station accordingto an embodiment of the present invention; and

FIG. 17 is a diagram showing an internal structure of a UE according toan embodiment of the present invention.

MODE FOR CARRYING OUT THE INVENTION

Hereinafter, embodiments of the present disclosure will be described indetail with reference to the accompanying drawings.

In describing the exemplary embodiments of the present invention,descriptions related to technical contents which are well-known in theart to which the present invention pertains, and are not directlyassociated with the present invention, will be omitted. Such an omissionof unnecessary descriptions is intended to prevent obscuring of the mainidea of the present invention and more clearly transfer the main idea.

For the same reason, in the accompanying drawings, some elements may beexaggerated, omitted, or schematically illustrated. Further, the size ofeach element does not entirely reflect the actual size. In the drawings,identical or corresponding elements are provided with identicalreference numerals.

The advantages and features of the present invention and ways to achievethem will be apparent by making reference to embodiments as describedbelow in detail in conjunction with the accompanying drawings. However,the present invention is not limited to the embodiments set forth below,but may be implemented in various different forms. The followingembodiments are provided only to completely disclose the presentinvention and inform those skilled in the art of the scope of thepresent invention, and the present invention is defined only by thescope of the appended claims. Throughout the specification, the same orlike reference numerals designate the same or like elements.

Here, it will be understood that each block of the flowchartillustrations, and combinations of blocks in the flowchartillustrations, can be implemented by computer program instructions.These computer program instructions can be provided to a processor of ageneral purpose computer, special purpose computer, or otherprogrammable data processing apparatus to produce a machine, such thatthe instructions, which execute via the processor of the computer orother programmable data processing apparatus, create means forimplementing the functions specified in the flowchart block or blocks.These computer program instructions may also be stored in a computerusable or computer-readable memory that can direct a computer or otherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer usable orcomputer-readable memory produce an article of manufacture includinginstruction means that implement the function specified in the flowchartblock or blocks. The computer program instructions may also be loadedonto a computer or other programmable data processing apparatus to causea series of operational steps to be performed on the computer or otherprogrammable apparatus to produce a computer implemented process suchthat the instructions that execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

And each block of the flowchart illustrations may represent a module,segment, or portion of code, which includes one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that in some alternative implementations, thefunctions noted in the blocks may occur out of the order. For example,two blocks shown in succession may in fact be executed substantiallyconcurrently or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

As used herein, the “unit” or “module” refers to a software element or ahardware element, such as a Field Programmable Gate Array (FPGA) or anApplication Specific Integrated Circuit (ASIC), which performs apredetermined function. However, the “unit” or “module” does not alwayshave a meaning limited to software or hardware. The “unit” or “module”may be constructed either to be stored in an addressable storage mediumor to execute one or more processors. Therefore, the “unit” or “module”includes, for example, software elements, object-oriented softwareelements, class elements or task elements, processes, functions,properties, procedures, sub-routines, segments of a program code,drivers, firmware, micro-codes, circuits, data, database, datastructures, tables, arrays, and parameters. The elements and functionsprovided by the “unit” or “module” may be either combined into a smallernumber of elements, “unit”, or “module” or divided into a larger numberof elements, “unit”, or “module”. Moreover, the elements and “units” or“modules” may be implemented to reproduce one or more CPUs within adevice or a security multimedia card.

A method for controlling transmission power by a UE in a mobilecommunication system includes: receiving a signal including transmissionresource allocation information and power control information from abase station; determining a signal transmission resource from which theUE is to transmit a signal based on the transmission resource allocationinformation; determining transmission power based on the power controlinformation according to the position of the determined signaltransmission resource; and transmitting the signal using the determinedtransmission power.

A method for supporting, by a base station, transmission power controlof a UE in a mobile communication system according to another embodimentof the present specification includes: transmitting a signal includingtransmission resource allocation information and power controlinformation to a UE; and receiving uplink transmission from the UE at aresource region determined according to the transmission resourceallocation information, wherein the UE determines a signal transmissionresource from which the UE is to transmit a signal based on thetransmission resource allocation information, determines transmissionpower based on the power control information according to the positionof the determined signal transmission resource, and transmits a signalusing the determined transmission power. In describing the exemplaryembodiments of the present invention, descriptions related to technicalcontents which are well-known in the art to which the present inventionpertains, and are not directly associated with the present invention,will be omitted. Such an omission of unnecessary descriptions isintended to prevent obscuring of the main idea of the present inventionand more clearly transfer the main idea.

An embodiment of the present specification relates to a method and anapparatus for controlling transmission power by a UE in transmitting adevice to device discovery signal by a UE between base stations in awireless cellular communication system, and includes a method forconfiguring transmission power in order to minimize the impact of noisedue to in-band emission of the UE and improve the performance of the UEdiscovery.

In addition, in describing embodiments of the present specification indetail, an Orthogonal Frequency Division Multiplexing (OFDM)-basedwireless communication system, in particular, the 3GPP Evolved UniversalTerrestrial Wireless Access (EUTRA) standard is regarded as a mainsubject. However, the main idea of the present specification can beapplied also to any other communication system having a similartechnical background and a channel shape with some modifications to theextent of not departing significantly from the scope of the presentinvention and the same can be possible by the decision of those skilledin the art of the present specification.

In embodiments of the present invention described below, a base stationor a cell may imply the same meaning. Further, Device to Device (D2D)communication may be used as a meaning including all of a discoveryoperation for discovering adjacent User Equipments (UEs) and directcommunication in which UEs directly exchange information.

FIG. 1 is a view showing a state where device to device communication(hereinafter referred to as D2D) is supported in a wirelesscommunication system according to an embodiment of the presentinvention.

Referring to FIG. 1, a base station 101 governs UEs 103, 104, and 105 ina cell 102 which is governed by the base station 101 itself. That thebase station 101 governs UEs 103, 104, and 105 may include providing awireless service. The UE 105 may perform cellular communication with thebase station 101 using a link 109 between the UE and the base station.

Further, the UEs 103 and 104 may perform cellular communication with thebase station 101 using links 107 and 108 between the UE and the basestation. In an embodiment, the cellular communication may includecommunication in which signals are transmitted and received between atleast one among the base station and the UE.

When the D2D communication between the UE 103 and the UE 104 ispossible, the UEs 103 and 104 may perform the discovery operation or thedirect communication operation using a D2D link 106 without passingthrough the base station 101.

A D2D technology using a cellular wireless mobile communication systemsuch as an LTE-A system can be supported in a direction not to causeproblems including interference of a UE in basically performingcommunication using the conventional cellular system.

In an embodiment, a method for performing communication so as not tomake interference between UEs which communicate using a D2D UE and acellular system, includes a method for performing communication using aresource, for D2D communication, which is separate from and notoverlapped with a wireless resource used by a cellular UE (a cellular UEof the present invention refers to a UE which includes a UE notperforming device to device communication but performing theconventional UE to base station communication). On the other hand,considered is a method for the D2D UE which uses the same resources usedby the cellular UE in a way to make as little interference as possiblewith each other.

A backward/forward duplexing method used by the LTE or LTE-A systemincludes a Frequency Division Duplexing (hereinafter referred to as FDD)method. The FDD may distinguish between forward transmission andbackward transmission by using frequency resources different from eachother. When a system using the FDD uses different resources for the D2Dcommunication and the conventional cellular communication, backwardfrequency resources are more preferentially used for the D2Dcommunication between forward and backward frequency resources ingeneral. This is because many more types of signals are multiplexed tothe forward frequency resources in comparison with the backwardfrequency resources. As a result, it is difficult to separately allocatethe forward frequency resources for the purpose of the D2D communicationin comparison with the backward frequency resources. Further, in the FDDsystem considering only the conventional cellular UE, forward traffic islarger than backward traffic due to the nature of a communicationservice and forwardly transmitted overheads are larger than backwardlytransmitted overheads, so that using the frequency for the forwardresources has a heavier burden in comparison with using the frequencyfor the backward resources. Accordingly, when the forward resourcesallocated for the purpose of the D2D communication are used, a burden ofthe forward resources becomes larger and thus it may be more difficultto adjust a balance between use of the forward and backward resources.

For the above reasons, an FDD communication system may use a reverse(directional) resource for D2D communication.

On the other hand, the above content is merely described as an advantagewhen using the reverse frequency resource as D2D resources, but itshould be noted that forward frequency resources may be used for the D2Dresources.

The next problem concerns a method for distinguishing between theconventional cellular communication resources and D2D communicationresources. Division of conventional cellular communication resources andD2D communication resources can be performed through an orthogonalscheme such as Time Division Multiplexing (hereinafter referred to asTDM) and Frequency Division Multiplexing (hereinafter referred to asFDM), and additionally, the distinction between the conventionalcellular communication resources and D2D communication resources isavailable through a non-orthogonal scheme reusing the same resource.

As described above, D2D communication can be supported in a way that theUE using the conventional cellular communication is not affected byproblem so that an orthogonal scheme is preferred for at least a UEdiscovery operation. In addition, preferably, a TDM scheme is preferredamong others for the UE discovery operation.

In an embodiment, the reason why the TDM scheme is preferred is that thebase station does not have to receive a cellular signal at a durationallocated by the D2D resources, by using the TDM scheme, and on theother hand, the D2D transmission is not present during a duration inwhich the cellular communication is transmitted. Therefore, the D2Dtransmission can minimize the impact of noise, etc. when performing thecellular communication.

FIG. 2 is a diagram showing a state where D2D transmission and cellulartransmission are multiplexed using a Time Division Multiplexing (TDM)scheme according to an embodiment of the present invention.

Referring to FIG. 2, reference numerals 201, 202, and 203 show that acellular sub-frame and D2D sub-frame are time-based TDM.

The cellular communication can be configured for the duration of thereference numeral 201 and the D2D transmission can be configured for thedurations of the reference numerals 202 and 203.

The durations of the reference numerals 202 and 203 can be referred as adiscovery duration 205, and the period in which the discovery durationis generated can be referred as a discovery period 204.

Discovery signals are multiplexed in the discovery duration 205including one or more reference numerals 202 and 203, and also aphysical uplink control channels (PUCCHs) 207 and 208 of the cellular UEmay be present in the discovery duration so as to transmit a responsefor Hybrid Automatic Retransmit reQuest (HARQ), Scheduling Request (SR),and Channel State Information (CSI) of the forward cellularcommunication. According to an embodiment, a PUCCH such as referencenumeral 207 and 208 may be present at both ends of the frequency area inthe discovery duration.

When discovery signals rather than the PUCCH in the discovery duration205 are to be multiplexed, resources for a plurality of discoverysignals from a section of reference numeral 206, that is, DiscoveryResource Block (hereinafter DRB) can be multiplexed in a time-frequencydomain. According to an embodiment, a DRB may be defined in atime-frequency unit of any size and may be multiplexed by forming a gridby a plurality of DRBs within the discovery duration such as referencenumeral 206. For example, one DRB can be defined by one sub-frame and 12sub-carriers (one RB), the same as a PRB. Any UE may transmit discoverysignals thereof to a single DRB in the multiplexed DRB.

Meanwhile, according to an embodiment, a plurality of UEs may transmitthe discovery signal to the single DRB. The UE may determine a DRB totransmit the discovery signal of the UE based on any rule or apredetermined rule, and any UE may transmit the discovery signal usingthe determined DRB.

For example, a UE 1 transmits a discovery signal of the UE 1 using a DRBof reference numeral 211, a UE 2 transmits a discovery signal of the UE2 using a DRB of the reference numeral 212, a UE 3 transmits a discoverysignal of the UE 3 using a DRB of reference numeral 213, and a UE 4transmits a discovery signal of the UE 4 using a DRM of referencenumeral 214. According to an embodiment, the correspondence between UEsand DRB may be relatively determined.

In an embodiment, when the UE 1 to UE 4 transmit discovery signals inthe same time duration (same sub-frame), sometimes each UE may notreceive the discovery signal from another UE. That is, the UE 1 may notreceive the discovery signal from the UE 2 to UE 4, the UE 2 may notreceive the discovery signal from the UE 1, UE 3, and UE 4, the UE 3 maynot receive the discovery signal from the UE 1, UE 2, and UE 4, and theUE 4 may not receive the discovery signal from the UE 1 to UE 3. Assuch, in order to solve a problem of not receiving the discovery signalof the UEs for transmitting discovery signals in the same time duration,a time-frequency hopping method in which the location of the DRB variesin each discovery duration can be used.

In an embodiment, as shown by reference numerals 221 to 224, thepositions of the DRB 1 to DRB 4 are different from the positions of theprevious discovery durations, and thus the UE 1 to UE 4 may receivediscovery signals from one another. As such, the DRBs are differentlyplaced in different positions in time and frequency according to thediscovery duration so that any UE may receive a discovery signal ofanother UE in the next discovery duration, and the discovery signal ofanother UE may not be received in the previous discovery duration.According to an embodiment, a time-frequency hopping method may bedetermined by one or more methods among a method configured in the UEand a method including a message, etc. received from a base station.

In the above, multiplexing between a D2D discovery signal and cellulartransmission, multiplexing between discovery signal resources indiscovery duration and a method of changing the position of the same DRBin accordance with the discovery duration were described. In thefollowing, a problem due to in-band emission power in a D2D operationwill be described.

In an embodiment, the UE transmits a discovery signal using one DRB, butwhen performing transmission in a full frequency band using anyfrequency block, in band other than the frequency block, a transmissionpower having a relative value with respect to the transmission powerused in the frequency block may be generated. This is referred to asre-emission power.

That is, with reference to FIG. 2, when the UE 1 transmits the discoverysignal of 23 dBm from the DRB1 211, −7 dBm power having, for example, 30dB difference from the transmission power of the DRB1 may be generatedin a DRB other than the DRB1 211 in the same sub-frame, and thegenerated power may result in acting as additional noise or interferenceto another UE which performs signal transmission and reception in theregion. Hereinafter, the nature of in-band emission power will bedescribed with reference to FIG. 3.

FIG. 3 is a diagram showing emission power when transmitting a signal bya UE according to the embodiment of the present invention.

More specifically, FIG. 3 shows a method for generating an in-bandemission power within a full band in an embodiment. Referring to FIG. 3,a diagram shows a smaller value than a value shown in the embodiment asthe requirement of the in-band emission power. In a case where the poweris applied in reality, the power may have the same in-band emissionpower as FIG. 3.

The horizontal axis 301 of FIG. 3 indicates PRB index, that is afrequency axis, and the vertical axis 302 indicates a magnitude ofrelative transmission power.

When transmitting data using any transmission power in PRB #7, as shownby reference numeral 303, which is a frequency allocated in theembodiment, −30 dB of transmission power is generated in the full bandas shown by reference numeral 307, and to two or three PRBs near theallocated frequency, as shown by reference numeral 304, −30 dB orgreater transmission power may be formed, and more specifically,transmission power may be generated in two or three PRBs adjacent to theallocated frequency in a stepwise manner.

In addition, as shown by reference numeral 305, additional emissionpower due to carrier leakage may be generated from at least one of PRB#24 and #25 positioned in the middle at the full band, and thustransmission power having a value greater than −30 dB may be generated.

In addition, an image frequency of the allocated frequency, as shown byfrequency reference numeral 306, that is, additional transmission powerdue to IQ imbalance may be generated in a frequency in the symmetricalposition relative to the intermediate frequency and thus transmissionpower greater than −30 dB may be generated. In an embodiment, since PRB#7 is an allocated frequency, additional emission power according to theIQ imbalance may be generated in PRB #42.

In an embodiment, when any UE transmits a discovery signal using anyDRB, in-band emission power may also be generated in bands other thanthe band to which the DRB is transmitted, due to one or more of theabove factors, and may affect discovery signals of other UEs, or affectthe transmission performance of a PUCCH located near the discoverysignal resource to be transmitted.

In other words, when the UE 103 and UE 104 of FIG. 1 transmit thediscovery signal using any frequency resource 1, the UE 105 may transmitthe PUCCH to the base station 101 using another frequency resource 2. Atthis time, when the distance between the UE 103 which transmits thediscovery signal and the base station 101 is closer than the distancebetween UE 105 and the base station 101, the transmission loss of asignal transmitted to the base station 101 from the UE 103 may besmaller than the transmission loss of the UE 105.

Therefore, in a state where the base station 101 may receive a PUCCHsignal of the UE 105 using a frequency resource 2, due to in-bandemission power generated from the discovery signal transmitted by the UE103 through a frequency resource 1 and a transmission loss difference,the reception power from the UE 103 may be greater than or similar tothe PUCCH signal of the UE 105 received through the frequency resource2. That is, the performance of the cellular UE may be deteriorated dueto the D2D discovery operation.

Accordingly, in order to prevent performance degradation of the uplinkcontrol signal of the cellular UE, the transmission power control of theD2D UE, including the discovery signal transmission of the D2D UE, maybe necessary. That is, in a case where the D2D UE is relatively closerto the base station, the D2D UE allows the transmission to use lesspower than defined transmission power. At this time, the transmissionpower when transmitting the discovery signal by the UE may be configuredas a predetermined value such as a maximum transmission power of the UE,a value defined through signaling by a wireless network including a basestation, a value configured in consideration of the transmission losswith the base station, and a value configured by the combination of theabove methods.

For example, the transmission power of the D2D UE may be determined byequation (1) as follows:

Tx_Power=min{Max_Tx_Power, f(D2D), g(PL)}  (1)

In the above equation (1), Max_Tx_Power is the maximum available powerof the transmission D2D UE, f(D2D) is transmission power, which isdetermined by the service type of the discovery signal transmitted bythe UE, and g (PL) is transmission power determined according to a powerloss (PL) between the base station and the UE. The g(PL) can bedetermined by equation (2) as follows:

g(PL)=Target_Rx_Power+PL  (2)

In the above equation (2), Target_Rx_Power is a target value of thereception power received, by the base station, from the UE. In addition,the transmission power of the UE may be configured by the above equation(2) by considering an offset value in consideration of carrier leakage.

As described above, when the transmission power is configured by thebase station based on a target value of the reception power receivedfrom the UE and the transmission loss between the UE and the basestation, the above problems can be solved.

However, when configuring the transmission power using a transmissionloss between the UE and the base station as described above, a D2D UE ata closer distance with the base station may transmit a discovery signalthereof always using lower transmission power than the D2D UE which isrelatively far from the base station. In other words, because the D2D UEwhich is adjacent to the base station as described above alwaystransmits the discovery signal at a low transmission power, the coverageof the discovery signal is limited. Therefore, the UEs as describedabove have difficulty in performing a correct D2D discovery operation.

Therefore, an embodiment of the present specification proposes a methodfor reducing performance degradation and deterioration of the D2Dcommunication performance, due to in-band emission power, through thetransmission power control, and increasing the overall performance, andthe method will be described with reference to examples.

Embodiment 1 A Periodic Discovery Signal Transmission Power ControlMethod

In order to mitigate PUCCH interference of a cellular UE due to in-bandemission power, D2D UEs in close proximity to the base station asmentioned above, may transmit discovery signals thereof using lowertransmission power through the power control. However, the power controlmethod enables discovery signals thereof to be transmitted to specificD2D UEs as described above according to the position of the basestation, using lower transmission power through the transmission powercontrol for each discovery signal transmission so that D2D communicationperformance degradation due to the reduction of discovery signaltransfer regions of the UEs may occur.

Therefore, in order to reduce the performance degradation of the D2Dcommunication, a transmission power control operation may be performed,which is different from the transmission power control method which isperiodically (T_(PC)) and previously used by the UEs. Here, the T_(PC)is a period during which a separate power control operation isperformed, which is different from the power control operationpreviously in use, and the previously used power control operation maybe performed during the discovery signal transmission rather than thecorresponding period. At this time, an operation of not performingtransmission power for the discovery signal control may be included inthe period. For convenience of explanation, the embodiment 1 describesthat transmission power for the discovery signal control is notperformed during the period.

That is, as mentioned above, for a UE in which transmission power forthe discovery signal is reduced through a power control, the UE mayperiodically transmit a discovery signal thereof without power controlfor a cellular UE as the following equation (3).

Tx_Power=min{Max_Tx_Power, f(D2D)}  (3)

In the above equation (3), Max_Tx_Power is the maximum available powerof the transmission D2D UE, and f(D2D) is the transmission power, whichis determined by the service type of the discovery signal transmitted bythe UE. At this time, the equation (3) is only a single example in whichtransmission power for the discovery signal is determined by the D2D UE,and there may be various methods of determining the transmission powerfor the discovery signal of the D2D UE.

In addition, the base station may perform power control using thereception power target values (Target_Rx_Power) of one or more basestations. In other words, the UE may perform the power control usingTarget_Rx_Power which is previously used in a predetermined powercontrol period (T_(PC)) and other target reception power valueTarget_Rx_Power_T_(PC). That is, in the transmission power controlmethod for the discovery signal (Tx_Power=min{Max_Tx_Power, f(D2D),g(PL)}), for the power control period (T_(PC)), a Target_Rx_Power_T_(PC)may be configured to be larger than Target_Rx_Power so that thetransmission power for the discovery signal of the UE closer to the basestation can be increased, as described above.

Here, a method for controlling the transmission power of the UE may beincluded by controlling other parameters required by the power controlas well as by controlling the reception power target value of the basestation.

At this time, the base station may inform of power control informationsuch as the base station reception power target values in the configuredpower control period (T_(PC)) and the corresponding period to the UE byusing at least one of System Information Black (SIB) signaling, higherlayer signaling, and dynamic signaling. In addition, the UE may be awareof the value as determined in advance. Here, the power control period isan additional period for determining whether to perform an additionalpower control or a period used for the D2D UE such as the previouslyobtained period (for example, a discovery resource region re-discoveryperiod). In addition, the period may be configured with the number ofcellular UEs, the number of D2D UEs closer to the base station, themagnitude of a reception signal of the discovery signal transmissionregion measured by a base station, etc.

A UE having acquired the period may perform power control as defined inthe period, or may perform power control defiled by discovery signaltransmission after a constant offset (X).

X=(UE_ID mod T _(PC)))}  (4)

In the above equation (4), UE_ID means a UE identification number. Theabove mentioned UE identification number is any one of possible IDs, andmay include International Mobile Subscriber Identity (IMSI), TemporaryMobile Subscriber Identity (TMSI), Packet-Temporary Mobile SubscriberIdentity (P-TMSI), Cell-Wireless Network Temporary Identifier (C-RNTI),and the like. In addition, the offset value may be determined by usingother information having a UE-specific value as well as the UEidentification number.

FIG. 4 is a diagram for explaining an operation of performing powercontrol by a UE according to a discovery signal transmission powercontrol period.

Referring to FIG. 4, a more detailed operation will be described asfollows. The UE 1 and UE 2 which acquire the power control period (TPC)from the base station perform a power control operation according to theperiod, perform a previously used power control operation for discoverysignal transmission during discovery signal transmission durations 401,402, 403, 404, and 405, and performs, during a period corresponding toT_(PC), a power control operation defined in the period.

For example, when defined so as not to perform power control during theperiod, both UE 1 and UE 2 which have reached a power control period(T_(PC)) during the duration 401 may transmit a discovery signal thereofwithout power control.

However, the UE 1 transmits a discovery signal after performing apreviously used power control operation by the offset value of theUE-specific in the duration 401 and does not perform the power controlin the duration 402. The UE 2, in the durations 401 and 402, transmits adiscovery signal after performing a previously used power controloperation as the operation in the duration 401 of the UE, and, in theduration 403, transmits the discovery signal without performing powercontrol.

As described above, since D2D UEs closer to the base station may alsotransmit discovery signals thereof without considering a cellular UEduring a particular discovery signal duration through embodiment 1, D2Dperformance degradation depending on the position of the UE can beprevented. Further, by dispersing the D2D UEs which perform powercontrol using the T_(PC) and the offset value as described above,in-band emission power effects on the cellular UE can be minimized.

Furthermore, in an embodiment, each UE may or may not perform powercontrol in the corresponding period based on a power control performingperiod offset value. More specifically, it is possible to perform thecontrol for reducing the transmission power in the conventionaldiscovery signal transmission duration. In addition, a control forincreasing the transmission power in the discovery signal transmissionduration, during the time duration corresponding to the power controlperforming period offset value, may be performed, and in accordance withan embodiment, a control for reducing the transmission power in thediscovery signal transmission duration, during the time durationcorresponding to the power control performing period offset value, maynot be performed.

Embodiment 2 A Discovery Signal Transmission Power Control MethodAccording to a Discovery Resource Region

In order to mitigate PUCCH interference of a cellular UE due to in-bandemission power, D2D UEs in close proximity to the base station, asmentioned above, may transmit discovery signals thereof using lowertransmission power through the power control. However, the above powercontrol method enables discovery signals thereof to be transmitted tothe specific D2D UEs according to the position of the base station,using lower transmission power through the transmission power controlfor each discovery signal transmission so that D2D communicationperformance degradation due to the reduction of discovery signaltransfer region of the UEs may occur.

In order to solve the above problem, the base station allocates aduration in which power control is not performed for the discoverysignal transmission in some resource regions among the D2D discoverysignal resource regions. In other words, the base station separates thediscovery signal resource region into one or more duration differenteach other and being operated so as to perform different power controlfor each duration to solve the above problem.

That is, the base station separates D2D resource regions by using one ormore target received powers, or a signal-to-interference plus noiseratio requirement, and enables the UE to perform different transmissionpower control operations for each resource region to solve the problem.

The UE may transmit discovery signal thereof using the D2D resourceregion allocated for D2D communication by the base station, and receivediscovery signals transmitted by adjacent UEs. At this time, the UE mayselect any one or a plurality of resources among the D2D resource regionand transmit a discovery signal thereof. On the other hand, the UE maymeasure the reception signal strength of all of the D2D resources orsome of the D2D resource regions, select a resource having the lowestsignal strength and transmit the discovery signal thereof, and selectany one among a resource candidate groups having low reception signalstrength.

In some cases, a UE for transmitting a discovery signal according to anembodiment may transmit the discovery signal in time or may not receivethe discovery signal from the another UE in time. Therefore, the UE mayselect any resource for each discovery signal transmission period orselect a different discovery resource for each discovery signaltransmission period using a predefined pattern (e.g., time-frequencyhopping) to transmit the discovery signal.

Therefore, the UE may use different discovery signal resources for eachdiscovery signal transmission period so that the above problem can beaddressed. That is, when the base station separates the D2D discoverysignal resource regions into one or more regions, and enables each ofthe UEs to perform different power control operations in each region,the UEs may perform a different power control operation for eachdiscovery signal transmission period. For example, the D2D discoveryresource region configured by one or more sub-frames may be separatedinto one or more sub-frame sets, and a different transmission powercontrol method for each sub-frame set may be used.

At this time, the base station may use the reception signal strengthrequirement or the signal-to-interference-noise ratio requirementreceived from the UE to perform different power control operations foreach sub-frame. At this time, not performing a separate power controloperation for the cellular UE may be a method for a power controloperation.

That is, the UE may perform a discovery signal transmission powercontrol operation according to the power control corresponding to adiscovery resource region determined for each discovery signaltransmission period.

FIG. 5 is a diagram for explaining a power control operation by a UE fora discovery resource region separated according to two transmissionpower control methods which are different from each other.

Referring to FIG. 5, from the perspective of the UE, a more specificpower control operation by the UE is described as follows. In anembodiment, the base station may perform one or more different powercontrols on resource regions of reference numerals 502 and 503, forexample, by separating a D2D discovery signal transmission area 501. Forexample, reference numeral 502 is a region for performing, by the UE,the discovery signal transmission power control operation for thecellular UE, and reference numeral 503 is a region for not performing,by the UE, the discovery signal transmission power control operation fora cellular UE.

In FIG. 5, for the convenience of explanation, the area was separatedinto regions 502 for performing the power control operation for thecellular UE and region 503 with no power control. In the control methodaccording to the embodiment, reference numeral 503 may include at leastone of no power control and performing a power control operationdifferent from the reference numeral 502. In other words, the discoveryresource area division according to the power control is to distinguishthe performance of one or more different power control operations by theUE, and no power control is also a part of the power control operation.

When the UE selects its own discovery signal transmission resource area504 in FIG. 5, the discovery signal of the UE is transmitted accordingto the transmission power control method of the power control region502. When the UE uses the region of the reference numeral 505 as its owndiscovery signal transmission resource, the discovery signal of the UEis transmitted according to the transmission power control method of thepower control region 503.

As shown in FIG. 5, when not performing transmission power control forthe cellular UE in the region 503, the UE may transmit a discoverysignal without performing a separate transmission power controloperation for the cellular UE. Throughout the embodiment, thetransmitting of the discovery signal by the UE without performing aseparate transmission power control operation may include transmittingthe discovery signal by the UE with a maximum transmission power orpower close thereto.

Through the above method, when the region for performing power controlas shown in the region 502 of FIG. 5 is to be selected for discoverysignal transmission resource, a D2D UE adjacent to the base station,according to a discovery signal resource region-specific transmissionpower control method by the base station, may perform power control inorder to minimize interference to a PUCCH region 506 of the UE forperforming cellular communication, and when there is no power controlregion as shown in the region 503 of FIG. 5, may transmit a signal whileperforming power control for the PUCCH. Thus, unlike the conventionalpower control method, since the D2D UE adjacent to the base station isnot always performing power control, the discovery signal performancedegradation of the D2D UE can be reduced.

In addition, since the duration such as reference numeral 503 is aregion in which the base station configures the power controlinformation according to its own state, the cellular UE may be awarethat the performance of the cellular UE will be degraded in the resourceregion 507 in which a control signal is transmitted by the cellular UE.Therefore, the base station may control the cellular UE so as not to usethe region or minimally use the region through the scheduling andresource allocation, etc. That is, the base station may configure theoperation of the cellular UEs on the regions by using information on theperformance difference between the cellular UEs in the regions ofreference numerals 506 and 507.

At this time, the power control information for each discovery signalresource region and a corresponding region may be informed of to the UE,by the base station, through a System Information Block (SIB), or thedownlink control channel, higher layer signaling, and dynamic signaling.In addition; the UEs may be aware of the information as a valuedetermined in advance. At this time, the information may includeposition (for example, time, frequency) information on the divideddiscovery signal resource duration and information and powercontrol-related parameters for each duration.

Embodiment 3 Method for Selecting a Discovery Signal Resource Accordingto the Position of a UE

In order to mitigate PUCCH interference of a cellular UE due to in-bandemission power, D2D UEs in close proximity to the base station asmentioned above, may transmit discovery signals thereof using lowertransmission power through the power control. However, the above powercontrol method enables discovery signals thereof to be transmitted tothe specific D2D UEs according to the position of the base station,using lower transmission power through the transmission power controlfor each discovery signal transmission so that D2D communicationperformance degradation due to the reduction of discovery signaltransfer region of the UEs may occur.

In order to solve the problem as described above, the base station maydivide the D2D discovery resource region into one or more regions basedon a predetermined criteria (e.g., based on a reception power of thediscovery signal from the base station or based on the position of a UE)and the D2D discovery resource region can be divided into one or moreregions. At this time, the UE enables the discovery signal thereof to betransmitted within the discovery signal region corresponding to the UEfrom among the reference regions configured by the base station so thatthe problem can be solved.

More specifically, the base station may measure reception power for thediscovery signal received from the D2D UE and divide the D2D discoveryresource into one or more regions. For example, the base station maydivide the D2D discovery resource into two regions based on receptionpower XdBm for the discovery signals of the D2D UEs received by the basestation. At this time, a reference may be configured by one of variousmeasurement values including a transmission path loss value between thebase station and the UE, Signal-to-Noise Ratio (SNR) orSignal-to-Interference plus Noise Ratio (SINR) as well as receptionsignal strength of the base station. Further, a reference value may beconfigured as a value capable of minimizing the PUCCH performancedeterioration of the cellular UE including the discovery signaltransmission by the D2D UE.

The reception power for discovery signals by D2D UEs of the base stationmay be used as the basis for the position of the D2D UE. That is, whenthe base station notifies a reference of the reception power from theD2D UEs to other UEs, the other UEs may predict the reception power ofthe base station on the discovery signal transmission by the UE, using apath loss value with the base station and the discovery signaltransmission power. That is, since the base station adjacent to the UEhas a relatively small path loss value, it is difficult to satisfy arequirement of the base station. In other words, reception power of thediscovery signals of the D2D UEs may be interpreted as reference Valuesfor the location of the UEs. The requirement may be determined based onthe magnitude of the reception power measured when the discovery signaltransmitted by the UE is received at the base station.

The reference value and the area for the control information may benotified of to the UE by the base station through the System InformationBlock (SIB), the downlink control channel, the higher layer signaling,or the dynamic signaling. In addition, the UEs may be aware of theinformation as a value determined in advance. At this time, theinformation may include position (e.g., time and frequency) informationon the divided discovery signal resource duration.

The UE which has acquired the reference value may predict the magnitudeof the discovery signal thereof received at the base station, by usingthe measured channel value such as path loss information between thebase station and the UE, and a transmission power value of the discoverysignal. Therefore, the UE may compare the information with referenceinformation configured by the base station to know its own discoverysignal transmittable region.

The UE having acquired the discovery signal transmittable region mayselect its own discovery signal from among one or more regions whichtransmits the discovery signal. At this time, the UE may select any oneresource or a plurality of resources among the discovery signaltransmittable region and transmit the discovery signal of the UE. On theother hand, the UE may measure the reception signal strength of all ofthe D2D resources or some of the D2D resource region, select a resourcehaving the lowest signal strength and transmit the discovery signalthereof, and select any one among a resource candidate group having lowreception signal strength. However, in some cases, a UE for transmittinga discovery signal according to an embodiment may not transmit thediscovery signal or may not receive the discovery signal from the otherUE in time. Therefore, the UE may select any resource for each discoverysignal transmission period, or select discovery resources different fromeach other among the discovery signal transmittable region for eachdiscovery signal transmission period using a predefined pattern (e.g.,time-frequency hopping) to transmit the discovery signal. At this time,when changing the discovery signal transmission resource using apre-defined pattern, the time-frequency hopping pattern may be formedaccording to the same discovery signal transmitted area.

As described above, the base station operates the D2D discovery resourceregion by dividing the discovery signal transmittable area using apredetermined reference so that the base station may predict aninfluence from the D2D UE. For example, the D2D discovery resourceregion configured by one or more sub-frames may be divided into one ormore sub-frames set so that D2D UEs adjacent to the base station and D2DUEs far from the base station may transmit a discovery signal in thesub-frames set different from each other. Therefore, the base stationmay know in advance the information that the performance of the cellularUE will be degraded due to the interference caused by the discoverysignal, in the resource region of a sub-frame set for transmitting thediscovery signal by the D2D UE close to the base station. At this time,the base station may control the cellular UE so as not to use the regionor minimally use the region through the scheduling and resourceallocation, etc. That is, the base station may configure the operationof the cellular UEs on the regions by using information on theperformance difference between the cellular UEs in the regions dividedby the reference.

FIG. 6 is a diagram for explaining a power control operation by a UE fora discovery resource region which is divided based on the position of aUE.

Referring to FIG. 6, from the perspective of the UE, a more specificpower control operation by the UE will be described as follows.

In an embodiment, the base station may divide the D2D discovery signaltransmission area 601 based on the reference on the position of one ormore UEs, such as regions 602 and 603. For example, the referencenumeral 602 is a region for performing the discovery signal transmissionby a UE of which a distance between the base station and the UE isfarther than the reference point, and the reference numeral 603 is aregion for performing the discovery signal transmission by a UE of whicha distance between the base station and the UE is closer than thereference point. In the embodiment, the discovery resource region isdivided based on the location of the UE for convenience of explanation,however information capable being received or measured from the UE bythe base station, such as the discovery signal strength of a D2D UEreceived from the base station, can be used as a reference or measured.In an embodiment, a distance between the base station and the UE may bedetermined based on a channel state between the base station and the UE.

In FIG. 6, a UE, which determines that a distance from the base stationis farther than a configured reference point, selects a discovery signaltransmission resource thereof in a remaining region 602 except for aregion indicated by reference numeral 603. For example, the UE selects aregion of the reference numeral 604 within the region of referencenumeral 602 and transmits the discovery signal thereof. However, a UE,which determines that a distance from the base station is closer than aconfigured reference point, selects discovery signal transmissionresource thereof in a remaining region 603 except for a region indicatedby reference numeral 602. For example, the UE selects a region of thereference numeral 605 within the region of reference numeral 603 andtransmits the discovery signal thereof.

At this time, when performing the discovery signal transmission using apre-defined pattern (time-frequency hopping), the UE, which hasperformed the discovery signal transmission in one region among theregion 602 of the D2D discovery signal transmission duration 601, may bedefined so as to select one of the discovery signal regionscorresponding to the reference, such as 602, in a D2D discovery signaltransmission duration 608. In addition, the UE, which has performed thediscovery signal transmission in one region among the region 603 of theD2D discovery signal transmission duration 601, should be defined so asto select one of the discovery signal regions corresponding to thereference, such as 603, in the D2D discovery signal transmissionduration 608. In other words, the time-frequency hopping pattern may bedefined such that one of the discovery signal resources within the samedivided region is selected for each D2D discovery signal transmissionduration.

Through the above mentioned method, since only the D2D UEs, which arefarther from the base station according to the reference pointconfigured by the base station, may transmit the discovery signal in theregion 602, the impact on a PUCCH region 606 of the UE for performingthe cellular communication can be minimized. However, since D2D UEsrelatively closer to the base station, in the duration such as theregion 603, may transmit the discovery signal, the performance of aPUCCH region 607 of the UE for performing the cellular communication canbe degraded. However, the base station may know in advance theinformation that the performance of the cellular UE in the region 607will be degraded according to the reference point configuration.Therefore, the base station may control the cellular UE so as not to usethe region or minimally use the region through the scheduling andresource allocation, etc. so that the impact on the cellular UE can beminimized.

Embodiment 4 A Discovery Signal Transmission Power Control MethodAccording to a Discovery Signal Transmission Resource Region

In order to mitigate PUCCH interference of a cellular UE due to in-bandemission power, D2D UEs in close proximity to the base station asmentioned above, may transmit discovery signals thereof usingtransmission power lower than the maximum transmitted power through thepower control. However, the power control method as described aboveallows discovery signals to be transmitted to specific D2D UEs accordingto the position of the base station, using lower transmission power foreach discovery signal transmission through the transmission powercontrol so that D2D communication performance degradation of the UEs mayoccur.

In order to solve the problem, the base station may notify of discoverysignal transmission power control information in each D2D sub-frame,using a downlink control channel to the UE. Thus, the base station maysolve the problem by being able to dynamically control the transmissionpower for the discovery signal of the D2D UE area according to the PUCCHtransmission of a cellular UE.

More specifically, the base station may configure, in each discoverysignal transmission area, transmission power control information ondiscovery signal transmission areas of the D2D UEs according to theinformation on the cellular UE. That is, when there is no PUCCHtransmission by the cellular UE in some of the sub-frame among thediscovery signal transmission area, at that time, the base station UEmay notify using a downlink control channel that the D2D UE may transmita discovery signal using a transmittable power without considering thecellular UE.

In addition, when there is PUCCH transmission by the cellular UE in somesub-frames of the discovery signal transmission area, the base stationmay control the discovery signal transmission power of the D2D UE tominimize the impact on the cellular UE.

The base station may configure transmission power control informationfor the discovery signal transmission area to the UE, using a downlinkcontrol channel such as a new Downlink Control Information (DCI) formatfor the D2D. The DCI format may include other information for D2D UEssuch as the information on the discovery signals of the D2D UEs as wellas the discovery signal transmission power control information.

FIG. 7 is a diagram explaining an operation of controlling, by a basestation, a discovery signal transmission power of a UE for downlinkcontrol channel information.

Referring to FIG. 7, from the perspective of the UE, a more specificpower control operation by the UE is described as follows.

In an embodiment, a D2D discovery signal transmission area 701 of thebase station may include a plurality of sub-frames. At this time, asub-frame may be formed of a control signal transmission section 702 anda data signal transmission section 703. Therefore, the base station maycontrol the transmission power of the D2D UE through transmitting acontrol signal in each sub-frame of the area 701. For example, in thesub-frame including reference numerals 702 and 703, when it isdetermined that there is no PUCCH transmission of the cellular UE orthat PUCCH performance deterioration of the cellular UE is small, thebase station enables the UE to perform a power control on the sub-framewithout considering the cellular UE through control signal transmissionof the reference numeral 702. At this time, the UE may select adiscovery resource in a reference numeral 707 region and transmit thediscovery signal without a separate power control for the cellular UE.However, when PUCCH transmission of the cellular UE is performed in thesub-frame configured by reference numerals 704 and 705, the base stationenables the UE to perform power control in consideration of the cellularUE in the sub-frame through control signal transmission of the referencenumeral 704. Therefore, the UE may select a discovery resource in areference numeral 708 region and transmit the discovery signal afterperforming a power control operation for the cellular UE.

At this time, the control information signal may include additionalinformation (for example, discovery signal transmission resource area)on the discovery signal transmission, including a configuration valuefor the power control of the D2D UE.

Through the method as described above, since the D2D UE may controldiscovery signal power according to the configuration of the discoverysignal power control of the base station, the impact on the PUCCHregions 706 and 709 of the UE for performing cellular communication canbe minimized. In addition, for a UE adjacent to the base station, sincethe discovery signal can be transmitted without any additional powercontrol according to the power control setting for the base station, aproblem of the performance deterioration due to the power controloperation for a cellular UE can be solved.

FIG. 8 is a flow chart illustrating an operation of a base stationaccording to a first embodiment of the present invention.

Referring to FIG. 8, in step 801, the base station begins an operation.

In step 802, the base station may set power control period informationand power control information on the period. According to an embodiment,the power control period information may include at least one of aperiod value for performing power control and offset information. Inaddition, the power control information may include a value that is thebasis for controlling transmission power for transmitting a discoverysignal by the UE.

In step 803, the base station may signal, to the UE, the configuredpower control period and power control information. More specifically,the base station may signal the configured power period informationthrough at least one of SIB signaling, RRC signaling, and dynamicsignaling to the UE.

In step 804, the base station ends the operation.

FIG. 9 is a flow chart illustrating an operation of a UE according to afirst embodiment of the present invention.

Referring to FIG. 9, in step 901, the UE begins an operation.

In step 902, the UE may receive a power control period and power controlinformation on the period from a base station. Step 902 may beselectively performed according to an embodiment, and when the step 902is not performed, the UE may use the configured information withoutreceiving the power control information from the base station.

In step 903, the UE configures a DRB for transmitting a discovery signalthereof in any discovery duration. The DRB configuration may bedetermined according to the DRB position determined by the UE or thebase station, and the position of each transmission DRB may be differentdepending on the application of the frequency hopping.

In step 904, the UE sets a power control period offset according to theconfigured DRB and power control period and sets a reference power byusing the power control information in the period. The power controlperiod offset information may be determined according to informationreceived in step 902 or a preconfigured UE information.

In step 905, the UE performs a discovery signal transmission by usingthe configured transmission power.

In step 906, the UE ends the operation.

FIG. 10 is a flow chart illustrating an operation of a base stationaccording to a second embodiment of the present invention.

Referring to FIG. 10, in step 1001, the base station begins anoperation.

In step 1002, the base station may divide and configure the discoveryresource region according to the power control information.

In step 1003, the base station may signal, to the UE, at least one ofinformation on the configured discovery resource region and powercontrol information on the region. More specifically, the base stationmay signal, to the UE, the configured power control information throughat least one of SIB signaling, RRC signaling, and dynamic signaling.

In step 1004, the base station ends the operation.

FIG. 11 is a flow chart illustrating an operation of a UE according to asecond embodiment of the present invention.

Referring to FIG. 11, in step 1101, the UE begins an operation.

In step 1102, the UE may receive discovery resource region informationand power control information for each region from the base station. Inan embodiment, the discovery resource region information includesdiscovery resource transmission region information having differentpower control information performed therein. In addition, the powercontrol information may include the power control information performedin each discovery resource transmission region.

Step 1102 may be selectively performed according to an embodiment, andwhen the step 1102 is not performed, the UE may use the configuredinformation without receiving the power control information from thebase station.

In step 1103, the UE configures a DRB for transmitting a discoverysignal thereof in a discovery duration region. The DRB configuration maybe determined according to the DRB position determined by the UE or thebase station, and the position of each transmission DRB may be differentdepending on the application of the frequency hopping.

In step 1104, the UE sets the transmission power using the power controlinformation according to the configured DRB region.

In step 1105, the UE performs a discovery signal transmission by usingthe configured transmission power.

In step 1106, the UE ends the operation.

FIG. 12 is a flow chart illustrating an operation of a base stationaccording to a third embodiment of the present invention.

Referring to FIG. 12, in step 1201, the base station begins anoperation.

In step 1202, the base station may divide a discovery resource regionaccording to a reference of a reception signal or a reference on a UEposition, and configure a discovery resource transmission region.According to an embodiment, the UE location may be determined based onone or more of the magnitude of the reception power for receiving asignal transmitted by the UE, path loss, and an SINR value.

In step 1203, the base station may signal, to the UE, the configureddiscovery resource region information and region dividing referenceinformation. More particularly, the base station may signal to the UEthrough at least one among SIB signaling, RRC signaling, and dynamicsignaling. The region dividing reference information according to anembodiment may include a basis for selecting, by the UE, the discoverysignal transmission region resource for a specific region according tothe embodiment.

In step 1204, the base station ends the operation.

FIG. 13 is a flow chart illustrating an operation of a UE according to athird embodiment of the present invention.

Referring to FIG. 13, in step 1301, the UE begins an operation.

In step 1302, the UE may receive a discovery resource region and theregion dividing reference information from the base station. The step1302 may be selectively performed according to an embodiment, and whenthe step 1302 is not performed, the UE may use pre-configuredinformation. The reference information for dividing the region accordingto an embodiment may include a basis for selecting, by the UE, thediscovery signal transmission region resource for a specific regionaccording to the embodiment.

In step 1303, the UE selects a discovery signal transmittable areathereof based on the received reference signal region.

In step 1304, the UE configures a DRB for transmitting a discoverysignal thereof among the discovery signal transmittable region. Theconfiguration of the DRB may be determined according to thedetermination of the DRM position by the UE or the base station, theposition of each transmission DRB may be different depending on theapplication of the time-frequency hopping, but at this time, thetime-frequency hopping is performed within the discovery signaltransmission region selected in step 1303.

In step 1305, the UE transmits the discovery signal by using theconfigured DRB region.

In step 1306, the UE ends the operation.

FIG. 14 is a flow chart illustrating an operation of a base stationaccording to a fourth embodiment of the present invention.

Referring to FIG. 14, in step 1401, the base station begins anoperation.

In step 1402, the base station may configure the power controlinformation for the D2D signal transmission region according to thecellular UE. In an embodiment, the D2D UE may configure power controlinformation for the discovery signal region determined based on theinfluence of a cellular UE in the UE, according to the discovery signalin the resource region for transmitting the discovery signal. Accordingto an embodiment, the power control information for the discovery signalregion may include at least one of a method for controlling transmissionpower and a value of the transmission power in a specific resourceregion.

In step 1403, the base station signals the configured discovery resourceregion and power control information on the region to the UE.

In step 1404, the base station ends the operation.

FIG. 15 is a flow chart illustrating an operation of a UE according to afourth embodiment of the present invention.

Referring to FIG. 15, in step 1501, the UE begins an operation.

In step 1502, the UE receives power control information on a discoveryresource region from the base station. According to an embodiment, thepower control information for the discovery signal region may include atleast one of a method for controlling transmission power and a value ofthe transmission power in a specific resource region. The step 1502 maybe selectively performed according to an embodiment, and when the step1502 is not performed, the UE may use pre-configured information.

In step 1503, the UE configures a DRB for transmitting a discoverysignal thereof among a discovery signal transmittable region. The DRBconfiguration may be determined according to the DRB position determinedby the UE or base station, and the position of each transmission DRB maybe different depending on the application of the time-frequency hopping.

In step 1504, the UE sets transmission power for the discovery signalaccording to the received power control information. In step 1505, theUE transmits the discovery signal by using the configured DRB region andtransmission power. In step 1506, the UE ends the operation.

FIG. 16 is a diagram showing a configuration of a base station accordingto an embodiment of the present invention.

FIG. 16 is a block diagram illustrating an internal configuration of abase station according to an embodiment of the present invention. Asshown in FIG. 16, the base station of the present invention may includea transceiver 1601 And controller 1602.

The transceiver 1601 transmits and receives a signal to and from nodesof a wireless communication system through a wired or wirelessinterface. For example, the transceiver 1601 may transmit and receivecontrol information or data to and from a UE through the wirelessinterface.

The controller 1602 controls the signal flow between blocks for theoperation of the base station. For example, the controller 1602 maycontrol the sequence of operations for controlling transmission powerfor the discovery signal of the UE performing the D2D communication. Tothis end, the controller 1602 may further include a base station-relatedinformation management unit 1603.

The base station-related information management unit 1603 may control totransmit, to the UE, the base station-related information necessary forcontrolling transmission power for the discovery signal of the UEperforming the D2D communication. According to each embodiment of thepresent invention, the base station-related information management unit1603 may control to transmit, to the UE, additional transmission powercontrol information on the discovery signal region division and eachregion according to the position of DRB.

FIG. 17 is a block diagram illustrating an internal structure of a UEaccording to an embodiment of the present invention.

As shown in FIG. 17, a UE of the present invention may include atransceiver 1701 and controller 1702.

The transceiver 1701 transmits and receives signals to and from a basestation through a wireless interface. According to an embodiment of theinvention, the transceiver 1701 may receive D2D-related information ofthe serving base station.

The controller 1702 controls the signal flow between blocks for theoperation of the base station. The controller 1702 according to anembodiment of the present invention may select a discovery signal forperforming D2D communication based on the D2D information received fromthe serving base station and control the transmission power of theselected discovery signal. To this end, the controller 1702 may furtherinclude a resource selection unit 1703 and a power controller 1704.

A resource selection unit 1703 may receive information on the DRB regionfrom the base station, and select a transmission resource of thediscovery signal for performing D2D communication on the basis of thereceived information. Since the specific process for selecting aresource of the discovery signal is mentioned above, a detaileddescription thereof will be omitted.

The power controller 1704 may receive power control informationaccording to the DRB region from the base station, and controltransmission power of the discovery signal for performing D2Dcommunication on the basis of the received information. Since thespecific process for controlling a transmission power of the discoverysignal is mentioned above, a detailed description thereof will beomitted.

Although exemplary embodiments of the present invention have been shownand described in this specification and the drawings, they are used ingeneral sense in order to easily explain technical contents of thepresent invention, and to help comprehension of the present invention,and are not intended to limit the scope of the present invention. It isobvious to those skilled in the art to which the present inventionpertains that other modified embodiments on the basis of the spirits ofthe present invention besides the embodiments disclosed herein can becarried out.

1-16. (canceled)
 17. A method by a terminal in a mobile communicationsystem, the method comprising: receiving, from a base station, downlinkcontrol information related to a device to device (D2D) communication,the downlink control information comprising power control informationrelated to the D2D communication; identifying transmission power relatedto the D2D communication based on the downlink control information; andtransmitting at least one signal related to the D2D communication basedon the identified transmission power.
 18. The method of claim 17,wherein the power control information comprises an indicator, andwherein the transmission power is identified based on a maximumtransmission power of the terminal for the D2D communication if theindicator is a first predetermined value.
 19. The method of claim 17,further comprising: receiving, from the base station, at least oneinformation related to D2D communication.
 20. The method of claim 19,wherein the power control information comprises an indicator, andwherein the transmission power is identified based on a maximumtransmission power of the terminal for the D2D communication and the atleast one information related to the D2D communication if the indicatoris a second predetermined value.
 21. A method by a base station in amobile communication system, the method comprising: identifying downlinkcontrol information related to a device to device (D2D) communication;and transmitting, to a terminal, the downlink control informationcomprising power control information related to the D2D communication,wherein transmission power related to the D2D communication isidentified based on the downlink control information, and wherein atleast one signal related to the D2D communication is transmitted basedon the identified transmission power.
 22. The method of claim 21,wherein the power control information comprises an indicator, andwherein the transmission power is identified based on a maximumtransmission power of the terminal for the D2D communication if theindicator is a first predetermined value.
 23. The method of claim 21,further comprising: transmitting, to the terminal, at least oneinformation related to D2D communication.
 24. The method of claim 23,wherein the power control information comprises an indicator, andwherein the transmission power is identified based on a maximumtransmission power of the terminal for the D2D communication and the atleast one information related to the D2D communication if the indicatoris a second predetermined value.
 25. A terminal in a mobilecommunication system, the terminal comprising: a transceiver fortransmitting and receiving a signal; and a controller configured to:receive, from a base station, downlink control information related to adevice to device (D2D) communication, the downlink control informationcomprising power control information related to the D2D communication,identify transmission power related to the D2D communication based onthe downlink control information, and transmit at least one signalrelated to the D2D communication based on the identified transmissionpower.
 26. The terminal of claim 25, wherein the power controlinformation comprises an indicator, and wherein the transmission poweris identified based on a maximum transmission power of the terminal forthe D2D communication if the indicator is a first predetermined value.27. The terminal of claim 25, wherein the controller is furtherconfigured to receive, from the base station, at least one informationrelated to D2D communication.
 28. The terminal of claim 27, wherein thepower control information comprises an indicator, and wherein thetransmission power is identified based on a maximum transmission powerof the terminal for the D2D communication and the at least oneinformation related to the D2D communication if the indicator is asecond predetermined value.
 29. A base station in a mobile communicationsystem, the base station comprising: a transceiver for transmitting andreceiving a signal; and a controller configured to: identify downlinkcontrol information related to a device to device (D2D) communication,and transmit, to a terminal, the downlink control information comprisingpower control information related to the D2D communication, whereintransmission power related to the D2D communication is identified basedon the downlink control information, and wherein at least one signalrelated to the D2D communication is transmitted based on the identifiedtransmission power.
 30. The base station of claim 29, wherein the powercontrol information comprises an indicator, and wherein the transmissionpower is identified based on a maximum transmission power of theterminal for the D2D communication if the indicator is a firstpredetermined value.
 31. The base station of claim 29, wherein thecontroller is further configured to transmit, to the terminal, at leastone information related to D2D communication.
 32. The base station ofclaim 31, wherein the power control information comprises an indicator,and wherein the transmission power is identified based on a maximumtransmission power of the terminal for the D2D communication and the atleast one information related to the D2D communication if the indicatoris a second predetermined value.